The survival of bacteria at low temperatures has been a subject of study for many years. Bretz and Hartsell (1969) pointed out that many variables affect the survival of micro-organisms following exposure to sub-freezing temperatures. The variables were listed as the freezing and suspending medium, initial cell concentration, species of micro-organism, age of the culture or stage of growth of the cells, the rate of freezing and thawing, the period of time which elapses between thawing and plating and the composition of the diluent and of the plating medium. All these variables have been shown to affect the apparent numbers of viable micro-organisms after exposure to freezing temperatures. [...]

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